Introduction to RNA-seq: From experimental design to gene quantitation

Transcript

1. RNA-seq: From (good) experimental design to (accurate) gene expression abundance. Steve Munger Narayanan Raghupathy The Jackson Laboratory 21st Century Mouse GeneJcs 11 August 2016
2. Outline General overview of RNA-seq analysis. •  IntroducJon to RNA-seq •  The importance of a good experimental design •  Quality Control •  Read alignment •  QuanJfying isoform and gene expression •  NormalizaJon of expression esJmates
3. RNA-seq: Sequencing Transcriptomes ATGCTCA AGCTA TAGATGCTCA AGCTA ATGCTCA AGCTAATC ATGCTCA AGCTA AGTAGATGCTCA AGCTA ATGCTCA AGCTA ATGCTCA AGCTA ATGCTCA AGCTA TAGATGCTCA AGCTAATC AGCTAATCCTAG CTCA mRNA
4. ApplicaJons of RNA-seq Technology Differen'al Gene expression analysis GSM71019.CEL GSM71020.CEL GSM71021.CEL GSM71022.CEL GSM71023.CEL GSM71024.CEL GSM71025.CEL GSM71026.CEL GSM71028.CEL GSM71029.CEL GSM71030.CEL GSM71031.CEL GSM71032.CEL GSM71033.CEL GSM71034.CEL GSM71035.CEL 213087_s_at 218488_at 204607_at 212282_at 218070_s_at 222029_x_at 222240_s_at 217714_x_at 218514_at 202980_s_at 208886_at 220230_s_at 204702_s_at 204807_at 218445_at 208656_s_at 212980_at 214220_s_at 211152_s_at 221927_s_at 203353_s_at 221563_at 222016_s_at 201820_at 205401_at 210007_s_at 211834_s_at 204199_at 76897_s_at 215471_s_at 213506_at 203355_s_at 221496_s_at 217536_x_at 220586_at 203610_s_at 212926_at 206788_s_at 214657_s_at 218470_at 214484_s_at 207821_s_at 212686_at 208165_s_at 204156_at 213320_at 210281_s_at 202223_at 219281_at 218535_s_at 200706_s_at 217388_s_at 214889_at 219924_s_at 211732_x_at 204732_s_at 216342_x_at 221476_s_at 212039_x_at 200038_s_at 213377_x_at 208645_s_at 213227_at 218654_s_at 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5. ApplicaJons of RNA-seq Technology Novel exon discovery Annotated gene Evidence from RNA-seq
6. ApplicaJons of RNA-seq Technology Novel exon discovery
7. ApplicaJons of RNA-seq Technology exon1 exon2 exon3 Alterna've splicing Isoform 1 Isoform 2
8. ApplicaJons of RNA-seq Technology Mom Dad TAGATGCTCA AGCTAATCCTAG TAGATGCTCA AGCTAATCCTAG A G A A A ATGCTCA TAGATGCTCA AGCTA ATGCTCA AGCTAATC ATGCTCA AGCTA AGCTA A G G G ATGCTCA AGCTATCC ATGCTCA AGCTATCCT ATGCTCA AGCTA A A A ATGCTCA TAGATGCTCA AGCTA GCTCA AGCTAAT TGCTCA AGCTAA AGCTA A Allele-Specific gene Expression (ASE) PreferenJal expression of one allele over the other.
9. RNA-seq Work Flow Aligned Reads QuanJfied isoform and gene expression Sequencing Reads (SE or PE) RNA isolaJon/ Library Prep Study Design N
10. mRNA mRNA aZer fragmentaJon cDNA Adaptors ligated to cDNA Single/ Paired End Sequencing RNA-Seq Total RNA N
11. Know your applicaJon – Design your experiment accordingly •  How many reads? Read depth •  Single-end or Paired-end sequencing? •  Read length? •  How many samples? N
12. RNA-seq Experimental design •  DifferenJal expression of highly expressed and well annotated genes? –  Smaller sample depth; more biological replicates –  No need for paired end reads; shorter reads (50bp) may be sufficient. –  Beder to have 20 million 50bp reads than 10 million 100bp reads. •  Looking for novel genes/splicing/isoforms? – More read depth, paired-end reads from longer fragments. N
13. Good Experimental Design MulJplexing ReplicaJon RandomizaJon N Illumina flowcell
14. Two Illumina Lanes Bad Design RNA-Seq Experimental Design: RandomizaJon Experimental Group 2 Experimental Group 1 N
15. Two Illumina Lanes Bad Design RNA-Seq Experimental Design: RandomizaJon Experimental Group 2 Experimental Group 1 N Beder Design Mouse ENCODE reanalysis: hdp://f1000research.com/arJcles/4-121/v1
16. RNA-seq Work Flow Aligned Reads QuanJfied isoform and gene expression Sequencing Reads (SE or PE) RNA isolaJon/ Library Prep Study Design N
17. mRNA mRNA aZer fragmentaJon cDNA Adaptors ligated to cDNA Single/ Paired End Sequencing RNA-Seq Total RNA N
18. Index Sequence @HISEQ2000_0074:8:1101:7544:2225#TAGCTT/1 X-Y Coordinate in flowcell Flowcell lane and Jle number Instrument: run/flowcell id The member of a pair Millions and millions of reads… @HISEQ2000_0074:8:1101:7544:2225#TAGCTT/1 TCACCCGTAAGGTAACAAACCGAAAGTATCCAAAGCTAAAAGAAGTGGACGACGTGCTTGGTGGAGCAGCTGCATG + CCCFFFFFHHHHDHHJJJJJJJJIJJ?FGIIIJJJJJJIJJJJJJFHIJJJIJHHHFFFFD>AC?B??C?ACCAC>BB<<<>C@CCCACCCDCCIJ Phred Score: Q = -10 log10 P 10 indicates 1 in 10 chance of error 20 indicates 1 in 100, 30 indicates 1 in 1000, SN
19. •  FASTX-Toolkit –  hdp://hannonlab.cshl.edu/fastx_toolkit/ •  FastQC –  hdp://www.bioinformaJcs.babraham.ac.uk/projects/ fastqc/ NGS Data Preprocessing Quality Control: How to tell if your data is clean S RNA-seq Data: Zp://Zp.jax.org/dgau/MouseGen2016/ •  B6-100K.fastq and Cast-100K.fastq
20. Quality Control: How to tell if your data is clean Good data §  Consistent §  High Quality Along the reads Bad data §  High Variance §  Quality Decrease with Length S RNA-seq Data: Zp://Zp.jax.org/dgau/MouseGen2016/ •  B6-100K.fastq and Cast-100K.fastq
21. NGS Data Preprocessing Per sequence quality distribu'on Y= number of reads X= Mean sequence quality bad data Average data S
22. NGS Data Preprocessing Per sequence quality distribu'on Y= number of reads X= Mean sequence quality bad data Average data Good data S
23. Quality Control: Sequence Content Across Bases S
24. NGS Data Preprocessing K-mer content counts the enrichment of every 5-mer within the sequence library Bad: If k-mer enrichment >= 10 fold at any individual base posi'on
25. K-mer content Most samples
26. NGS Data Preprocessing Duplicated sequences Good: non-unique sequences make up less than 20% Bad: non-unique sequences make >50% S
27. Tradeoffs to preprocessing data •  Signal/noise -> Preprocessing can remove low- quality “noise”, but the cost is informaJon loss. –  Some uniformly low-quality reads map uniquely to the genome. –  Trimming reads to remove lower quality ends can adversely affect alignment, especially if aligning to the genome and the read spans a splice site. –  Duplicated reads or just highly expressed genes? –  Most aligners can take quality scores into consideraJon. –  Currently, we do not recommend preprocessing reads aside from removing uniformly low quality samples. S
28. RNA-seq Work Flow Aligned Reads QuanJfied isoform and gene expression Sequencing Reads (SE or PE) RNA isolaJon/ Library Prep Study Design S
29. Alignment 101 ACATGCTGCGGA ACATGCTGCGGA 100bp Read Chr 1 Chr 2 Chr 3 S
30. The perfect read: 1 read = 1 unique alignment. ACATGCTGCGGA ACATGCTGCGGA 100bp Read ✓ Chr 1 Chr 2 Chr 3 S
31. Some reads will align equally well to mulJple locaJons. “MulJreads” ACATGCTGCGGA ACATGCTGCGGA ACATGCTGCGGA ACATGCTGCGGA 100bp Read ✓ ✗ ✗ 1 read 3 valid alignments Only 1 alignment is correct S
32. Aligning Millions of Short Sequence Reads Gene A Gene B Aligners: BowJe, GSNAP, STAR, BWA, BLAT, HISAT2, BowJe2, Kallisto, Salmon N
33. Align to Genome or Transcriptome? Genome Transcriptome Advantages: Can align novel isoforms. Disadvantages: Difficult, Spurious alignments, spliced alignment, gene families, pseudo genes N
34. Align to Genome or Transcriptome? Genome Transcriptome Advantages: Easy, Focused to the part of the genome that is known to be transcribed. Disadvantages: Reads that come from novel isoforms may not align at all or may be misadributed to a known isoform. Advantages: Can align novel isoforms. Disadvantages: Difficult, Spurious alignments, spliced alignment, gene families, pseudo genes N
35. Output of most aligners: Bam/Sam file of reads and genome posiJons N
36. VisualizaJon of alignment data (BAM/SAM) Genome browsers – IGV and UCSC Integra've Genome Viewer (IGV) hdp://soZware.broadinsJtute.org/soZware/igv/download RNA-seq Data: Zp://Zp.jax.org/dgau/MouseGen2016/ •  DO.chr1XY.sorted.bam and DO.chr1XY.sorted.bam.bai
37. IGV is your friend. Read color = strand SNP Coverage density plot
38. Example genes to look at in IGV 1.  Tsn 2.  Gorab 3.  Fmo1, Fmo2, Fmo3, Fmo4, Fmo6 4.  Ids 5.  Zfx 6.  Ssty1, Ssty2
39. Aligned Reads to Gene Abundance Aligned Reads QuanJfied isoform and gene expression 100bp Reads Total RNA N
40. Aligned Reads to Gene Abundance: Challenges Long Short Many approaches to quanJfy expression abundance N
41. Long Short 200 Medium 100 50 1000 reads 1 2 3 RelaJve abundance for these genes, f1 , f2 , f3 Aligned Reads to Gene Abundance: Challenges N
42. Long Short 200 Medium 100 50 1 2 3 RelaJve abundance for these genes, f1 , f2 , f3 400 400 200 Aligned Reads to Gene Abundance: Challenges N
43. Long Short 200 Medium 100 50 1 2 3 RelaJve abundance for these genes, f1 , f2 , f3 350 300 200 150 Unique MulJreads MulJreads: Reads Mapping to MulJple Genes/Transcripts N
44. Approach 1: Ignore MulJreads Long Short 200 Medium 100 50 1 2 3 RelaJve abundance for these genes, f1 , f2 , f3 350 300 200 150 Nagalakshmi et. al. Science. 2008 Marioni, et. al. Genome Research 2008 N
45. Approach 1: Ignore MulJreads Long Short 200 Medium 100 50 1 2 3 350 300 200 150 •  Over-esJmates the abundance of genes with unique reads •  Under-esJmates the abundance of genes with mulJreads •  Not an opJon at all, if interested in isoform expression N
46. Approach 2: EM algorithm based allocaJon of MulJreads Long Short 200 Medium 100 50 1 2 3 RelaJve abundance for these genes, f1 , f2 , f3 350 300 200 150 RSEM, Cufflinks, isoEM, MMSEQ & eXpress N
47. Long gene 2 N Approach 2: EM algorithm based allocaJon of MulJreads gene 1 9 reads 1 read
48. Long gene 2 N Approach 2: EM algorithm based allocaJon of MulJreads gene 1 9 reads 1 read 0.9 0.1
49. ACATGCTGCGGA 100bp Read Chr 2 The rise of Pseduo-alignment a.k.a alignment-free methods Transcriptome K-mers Sailfish, Salmon, and Kallisto
50. ACATGCTGCGGA 100bp Read Running Jme in minutes Expression quanJtaJon for 30 Million Reads Kallisto: K-mer based pseudo-alignment
51. Conclusions for quanJtaJon •  EM approaches are currently the best opJon. •  Isoform-level esJmates are sJlll challenging and will become easier as read length increases. •  K-mer counJng methods (Salmon, Kallisto) are very fast – they can be run easily on your own PC – and are reasonably accurate. N
52. Expression Abundance: Counts, RPKM/FPKM, TPM Long Gene Short Gene Long Gene Short Gene Sample 1 Sample 2 FPKM Number of Fragments Matched to a Gene / Kilo base Total matched reads in Millions
53. NORMALIZATION A speed bump on the road from raw counts to differenJal expression. S
54. Large pool, small sample problem •  Typical RNA library esJmated to contain 2.4 x 1012 molecules. McIntyre et al 2011 •  Typical sequencing run = 25 million reads/sample. •  This means that only 0.00001 (1/1000th of a percent) of RNA molecules are sampled in a given run. •  High abundance transcripts are sampled more frequently. Example: Albumin = 13% of all reads in liver RNA-seq samples. •  Sampling errors affect low-abundance transcripts most. S
55. A finite pool of reads. S
56. Alb Low1 Sample 1 Alb Low1 Sample 2 Perfect world: All transcripts counted. S
57. Alb Low1 Sample 1 Real world: More reads taken up by highly expressed genes means less reads available for lowly expressed genes. S
58. Alb Alb Low1 Low1 Sample 1 Sample 2 Highly expressed genes that are differenJally expressed can cause lowly expressed genes that are not actually differenJally expressed to appear that way. S
59. NormalizaJon of raw counts •  Wrong way to normalize data – Normalizing to the total number of mapped reads (e.g. FPKM). Top 10 highly expressed genes soak up 20% of reads in the liver. FPKM is widely used, and problemaJc. •  Beder ways to measure data – Normalize to upper quarJle (75th %) of non-zero counts, median of scaled counts (DESeq), or the weighted trimmed mean of the log expression raJos (EdgeR). S
60. DifferenJal Expression Analysis Over-esJmaJon of Under-esJmaJon of ˆ2 g ˆ2 g Too conservaJve Too sensiJve (Many false posiJves) tg = ˆ µg,1 ˆ µg,2 s ˆ2 g,1 N1 + ˆ2 g,2 N2 DESEQ2, edgeR, Voom, & CuffDiff T-test Normal Cancer Expression
61. MulJple TesJng CorrecJon and False Discovery rate XKCD Significant 2012 IgNobel prize in Neuroscience for “finding Brain acJvity signal in dead salmon using fMRI” N
62. Single Cell RNA-seq Technologies Fluidigm C1 Chip 96 cells / 800 Cells DropSeq: 40,000 cells 10X Genomics: 48,000 cells
63. Summary ATGCTCA AGCTA TAGATGCTCA AGCTA ATGCTCA AGCTAATC ATGCTCA AGCTA AGTAGATGCTCA AGCTA ATGCTCA AGCTA ATGCTCA AGCTA ATGCTCA AGCTA TAGATGCTCA AGCTAATC AGCTAATCCTAG CTCA RNA
64. Summary ATGCTCA AGCTA TAGATGCTCA AGCTA ATGCTCA AGCTAATC ATGCTCA AGCTA AGTAGATGCTCA AGCTA ATGCTCA AGCTA ATGCTCA AGCTA ATGCTCA AGCTA TAGATGCTCA AGCTAATC AGCTAATCCTAG CTCA RNA Experimental Design RNA-seq analysis pipeline As sequences get longer, alignment and isoform quanJtaJon becomes easier!
65. Resources Aligner –  BowJe 2 hdp://bowJe-bio.sourceforge.net/bowJe2/index.shtml –  GSNAP hdp://research-pub.gene.com/gmap/ Transcript Discovery/AnnotaJon - STAR hdps://github.com/alexdobin/STAR/releases - Tophat hdp://tophat.cbcb.umd.edu/ Transcript Abundance –  Kallisto hdp://pachterlab.github.io/kallisto/ –  RSEM hdp://deweylab.biostat.wisc.edu/rsem/ –  EMASE hdps://github.com/churchill-lab/emase DifferenJal Expression –  DESeq hdp://www-huber.embl.de/users/anders/DESeq/ –  edgeR hdp://bioconductor.org/packages/release/bioc/html/edgeR.html –  EBSeq hdps://www.biostat.wisc.edu/~kendzior/EBSEQ/
66. Example 1 DifferenJal expression in my mutant mouse compared to wild type. What genes are up- or down-regulated?
67. Things to consider… •  DifferenJal expression of highly expressed and well annotated genes? –  Smaller sample depth; more biological replicates –  No need for paired end reads; shorter reads (50bp) may be sufficient. –  Beder to have 20 million 50bp reads than 10 million 100bp reads. •  Looking for novel genes/splicing/isoforms? – More read depth, paired-end reads from longer fragments. N
68. Example 2 •  How to quanJfy gene expression in a species that has not been sequenced or annotated? – MulJstep strategy using mulJple sequencing technologies.
69. Example 3 •  How to quanJfy single cell gene expression in a heterogeneous human tumor?
70. Any other applicaJons you are interested in? Steve Munger steven.munger@jax.org Narayanan Raghupathy narayanan.raghupathy@jax.org
71. Acknowledgements •  KB Choi •  Gary Churchill •  Ron Korstanje/ Karen Svenson/ Elissa Chesler •  Joel Graber •  Doug Hinerfeld •  Anuj Srivastava •  Churchill Lab – Dan Gau •  Al Simons and Mad Hibbs •  Lisa Somes, Steve Ciciode, mouse room staff at JAX •  Gene Expression Technologies group at JAX